Chaning kernel.shmmax value after more physical memory is added
 

Hi,

This is my first post.

Below is my system architect:

2.6.9-78.0.13.ELsmp #1 SMP Wed Jan 7 17:45:52 EST 2009 x86_64 x86_64 x86_64 GNU/Linux

We had an Oracle Database Server with 16G of RAM. We encountered performance issue, so we added additional 16G or RAM.

Please let me know how large can I set kernel.shmmax value to in the /etc/sysctl.conf file.

Oracle doc. suggested to set it to half of the physical memory. But I would like to know whether it can set to a larger value so that I can increase Oracle SGA_MAX_SIZE to boost my DB performance.

Thank you in advance for your advice.

princessshieh

http://www.idevelopment.info/data/Or.../LINUX_8.shtml

You should find that the above link, particularly Chapter 3, answers your question :)

If there's anything you don't understand after reviewing that section, feel free to ask for more detail.

Cheers!
Sasha

PS - Welcome to LinuxQuestions!

Hi Sasha,

Thanks for your reply.

The link provided herein did not answer my question.

Basically I like to know what value I can set shmmax given the fact that there are total of 32G physical memory on my system. I have two Oracle instances on that box. I allocated 15 G for one of the instances, but only 500M for the 2nd one. That leaves some physical memory unused, I guess.

Since I have total of 32G, I feel like that I should be able to allocate more SGA to my first instance. But I am not sure how much I can set it to? If I increase SGA, then, I should change shmmax kernel parameter as well, right.

Thanks,

Karin